shear pin breakage

[Highbeam]

"That in turn means you'll secure the slip clutch to the "tranny shaft" with a bolt, which - if the wrong grade is selected - will once again put you back in shear bolt territory."

BS again. The weak shear bolt is replaced by a strong retainer bolt according to the instructions with the slip clutch assembly. It may indeed shear if the slip clutch is improperly adjusted but perhaps the engine crankshaft will break too. Does that mean you now have a shear crank? No.

 

[Highbeam]

"That in turn means you'll secure the slip clutch to the "tranny shaft" with a bolt, which - if the wrong grade is selected - will once again put you back in shear bolt territory."

BS again. The weak shear bolt is replaced by a strong retainer bolt according to the instructions with the slip clutch assembly. It may indeed shear if the slip clutch is improperly adjusted but perhaps the engine crankshaft will break too. Does that mean you now have a shear crank? No.

 

[SPYDERLK]

Toby, so you have a smooth input shaft on the mower transmission. The pto yoke is pinned to this shaft with a bolt or shear pin. The problem in this type of set up is that there is always clearance between shaft and yoke even when new. As the shaft rotates there are torque fluctuations due to cyclic variations in speed caused by the u-joints as well as hitting things with the mower blades. The clearance allows the yoke to wobble a little on the shaft. This causes wear on the shaft, yoke and pin. The pin is expendable. Wear on the other parts is a serious matter and accelerates as clearance increases. Shearing pins just adds to the abuse of the inadequate design. This type of joint should be immobilized in some way or have a gease fitting so that movement is lubed and damped by the grease. I would not choose a shear pin on equipment that is used heavily and long term like a bushog. If I were stuck with this situation I would add a grease fitting. Shearing pins would drive me batty tho so I would ultimately go to a slip clutch. If I had your situation I would either add a fitting or loctite the yoke to the shaft, and put a slip clutch on. Just the clutch would fix the problem for awhile, but the yoke-shaft interface will continue to worsen if not immobilized or lubed.
Larry

 

[SPYDERLK]

Toby, so you have a smooth input shaft on the mower transmission. The pto yoke is pinned to this shaft with a bolt or shear pin. The problem in this type of set up is that there is always clearance between shaft and yoke even when new. As the shaft rotates there are torque fluctuations due to cyclic variations in speed caused by the u-joints as well as hitting things with the mower blades. The clearance allows the yoke to wobble a little on the shaft. This causes wear on the shaft, yoke and pin. The pin is expendable. Wear on the other parts is a serious matter and accelerates as clearance increases. Shearing pins just adds to the abuse of the inadequate design. This type of joint should be immobilized in some way or have a gease fitting so that movement is lubed and damped by the grease. I would not choose a shear pin on equipment that is used heavily and long term like a bushog. If I were stuck with this situation I would add a grease fitting. Shearing pins would drive me batty tho so I would ultimately go to a slip clutch. If I had your situation I would either add a fitting or loctite the yoke to the shaft, and put a slip clutch on. Just the clutch would fix the problem for awhile, but the yoke-shaft interface will continue to worsen if not immobilized or lubed.
Larry

 

[AlanB]

Clearly at this point you need to get the burr out, or whatever is holding that shaft up at the moment, and if that yoke is oblonged, then replace that, but if I am reading it correctly this has very little use and has only broken 4 shear bolts? I cannot imagine it being oblonged in that period of time.

Anyway, just a sideways thought, but something I would consider, and I may be reading more into your post then was there.

I get the impression that you got all these shear bolts at once, from one place.

I would try a bolt from a different source. still grade two or 5 or whatever howse called for, but a different batch / manufacturer. Just something to think about, and cheap and easy enough to do.

 

[AlanB]

Clearly at this point you need to get the burr out, or whatever is holding that shaft up at the moment, and if that yoke is oblonged, then replace that, but if I am reading it correctly this has very little use and has only broken 4 shear bolts? I cannot imagine it being oblonged in that period of time.

Anyway, just a sideways thought, but something I would consider, and I may be reading more into your post then was there.

I get the impression that you got all these shear bolts at once, from one place.

I would try a bolt from a different source. still grade two or 5 or whatever howse called for, but a different batch / manufacturer. Just something to think about, and cheap and easy enough to do.